1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting radio link failure (RLF) information in a wireless communication system.
2. Related Art
Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
Meanwhile, due to an in-device industrial, scientific and medical (ISM) transmitter, a 3GPP LTE radio can be interfered in case that the 3GPP LTE radio and an ISM radio coexist within the same device operating in adjacent frequencies. For example, when the LTE radio is working on band 40 and the ISM radio such as WLAN is active in a same device at the same time, the LTE radio in Rx mode is interfered by the ISM transmitter. Also, the transmission of the LTE radio can interfere the reception of the ISM/GNSS (global navigation satellite system) radio.
As a remedy for avoiding above in-device coexistence (IDC) interference, three possible LTE network-controlled user equipment (UE)-assisted solutions are suggested and captured in 3GPP TR 36.816, which are FDM, TDM, power control (PC) solution. From the LTE point of view, the FDM solution is to move the interfered LTE to another serving frequency. The TDM solution is to ensure that transmission of a radio signal does not coincide with reception of another radio signal. The PC solution is to reduce the LTE transmission power to mitigate the interference to ISM/GNSS receiver.
Depending on the solution, the necessary information included in the indication is different. For the FDM solution, the UE may indicate which frequencies are unusable due to in-device coexistence. For the TDM solutions, the UE may signal the necessary information, e.g. interferer type, mode, and possibly the appropriate offset in subframes to the eNB. The UE may also signal a suggested pattern to the eNB. For the PC solution, the UE may notify the network of interference type, power reduction value, etc.
Meanwhile, a radio link failure (RLF) may be occurred based on various reasons. The RLF may be occurred due to a radio resource control (RRC) connection reestablishment failure. In this case, RLF information is stored and is transmitted to the network. Or, the RLF may be occurred due to in-device coexistence (IDC) interference when the 3GPP LTE radio and an ISM radio coexist within the same device operating in adjacent frequencies. There is need to distinguish whether the RLF is triggered by interference from in-device ISM radio or not.
A method for restricting of storing and reporting RLF information based on in-device coexistence interference.